1. Field of the Invention
The present invention relates to a molded case circuit breaker, and particularly, to an arc extinguisher assembly for a molded case circuit breaker capable of improving current limiting performance by speedily cooling an arc generated in a procedure where the breaker interrupts an electric shortage current when a short circuit occurs.
2. Description of the Conventional Art
A molded case circuit breaker is an electrical device that protects a circuit and a load by automatically opening the circuit against an excess current such as an electric shortage current. A molded case circuit breaker that has an excellent arc extinguishing capability and can interrupt a current within a short period of time is considered to be the one with good current limiting performance.
Referring to FIGS. 1 to 4, an arc extinguisher assembly in accordance with the conventional art will now be described.
First, the construction of the molded case circuit breaker provided with the conventional arc extinguisher assembly will now be described with reference to FIG. 1 that illustrates a longitudinal sectional view thereof. The conventional molded case circuit breaker 100 includes a first fixed contactor 141 formed of a conductor and having a terminal portion connected to power source or an electrical load, and a movable contactor 142 being rotatively movable to a position where it comes in contact with the first fixed contactor 141 (hereinafter, referred to as a contacted position) or a position where it is separated from the first fixed contactor 141 (hereinafter, referred to as a separated position). The arc extinguisher assembly 140 for extinguishing an arc in accordance with the conventional art is installed to surround a contact portion between the first fixed contactor 141 and the movable contactor 142. In FIG. 1, reference numeral 150 designates a holder that rotatably supports the movable contactor 142, and reference numeral 120 designates a switching mechanism that rotatively drives the movable contactor 142 to the contacted position or the separated position. A second fixed contactor 160 is connected to the movable contactor 142 by an electrical conductor (not shown) and has at its one end portion, a terminal portion connected to power source or an electrical load. Reference numeral 170 represents a trip mechanism for triggering the switching mechanism 120 to operate to a trip position when a current flowing through the second fixed contactor 160 is an excessive current such as an electric shortage current. Reference numeral 180 represents a handle connected to the switching mechanism 120, for manually moving the movable contactor 142 to the contacted position or the separated position.
The detailed construction of the arc extinguisher assembly, the case, and the fixed and movable contactors in accordance with the conventional art, which are built in the molded case circuit breaker, will now be described with reference to FIG. 2.
FIG. 2 is an exploded perspective view that illustrates the arc extinguisher assembly, a portion of the case receiving the assembly, the fixed contactor and the movable contactor of FIG. 1 in detail.
The arc extinguisher assembly 143 is installed to surround contacts 141a and 142a of the fixed contactor 141 and the movable contactor 142. The arc extinguisher assembly 143 includes a plurality of plates 143a made of metal of a ferro magnetic material, an uppermost plate 144, and a support plate 143b made of an electrically insulated material and for supporting the plates 143a. 
The fixed contactor 141 is a current-limiting type one which is bent in a U-shape, and a fixed contact 141a is attached onto one end portion of the fixed contactor 141 by way of welding or the like. An arc runner 141b for inducing an arc is attached behind the fixed contact 141a on an upper portion of the fixed contactor 141.
In the drawing, the case 145 illustrated with deviant lines represents a portion of a case and a cover, which receives the arc extinguisher assembly, and is made by molding a synthetic resin having an electrical insulation property.
The arc extinguishing operation of the arc extinguisher assembly for a molded case circuit breaker in accordance with the conventional art will now be described with reference to FIGS. 3 and 4. FIG. 3 is a perspective view for describing the arc extinguishing operation by the arc extinguisher assembly of FIG. 1, and FIG. 4 is a view for describing moving directions of an arc in order to show a moving path of an arc in the arc extinguisher assembly of FIG. 3.
If an abnormal current such as an excessive current and an electric shortage current is generated in an electrical circuit in a state that the fixed contact 141a and the movable contact 142a are electrically connected, the movable contactor 142 is rotated to be separated from the fixed contactor 141 by an electro magnetic repulsive force created between the fixed contact 141a and the movable contact 142a, thereby opening the circuit.
When the movable contactor 142 is separated from the fixed contactor 141, an arc occurs between the fixed contact 141a and the movable contact 142a, and the arc generated thereby is induced to the arc runner 141b (refer to FIG. 2). Then, as shown in FIG. 4, some arc (a, b and c) moves toward the arc extinguisher assembly 143 and the rest flows back toward the contacts 141a and 142a. 
Then, the arc is divided and cooled by the plates 143a of the arc extinguisher assembly 143, thereby being extinguished. An arc gas formed as the air around the arc is heated is discharged to the outside of the molded case circuit breaker through an discharge hole 146 of FIG. 3.
However, in the conventional arc extinguisher assembly for a molded case circuit breaker, a column of the arc cannot be compressed and extended, and the arc is extinguished only by the effects of dividing and cooling by the plurality of laminated plates 143a. Thusly, it takes a long time to complete such extinguishing. Also, an arc may reoccur or the contacts 141a and 142a are damaged by a back flow of an arc and a gas around the arc toward the contacts 141a and 142a. 